Vulcanizing rubber



Patented June 7, 1932 GEORGE H. STEVENS, OF NEWARK, NEW JERSEYVULGANIZING RUBBER No Drawing. Original application filed July 16, 1923,Serial No. 651,968. Divided and this application filed August 25, 1927.Serial No. 215,511.

This invention relates to improvements in the use of organic,nitrogenous, substances that assist in or accelerate the vulcanizationof rubber.

This specification is a division of Ser. No. 651,968 filed July 16,1928, relating to combinations of monoand tri-substituted guanidines.

The object of this invention is the utilization of mono-phenylsubstituted carbodiimide, its polymers and homologues, with theguanidine products that result from the r reaction with ammonia, andwhich constitute the mono-substituted element in the combination that isthe parent invention.

Concurrent with the filing of this division of 651,968 a like divisionis also filed relating mainly to di-phenyl substituted carbodiimide, itspolymers and homologues, and the guanidine products that result fromtheir reaction with aniline, or with a primary monamine homologous toaniline.

In a previous application (Ser. No. 399,- 979), filed July 30, 1920, Imentioned monophenyl 'guanidine (C H N as a rubber accelerator, having anitrogen content of 31%. c

Mono-phenyl guanidine has a melting point of 66 C., is quitehygroscopic, is soluble in water, and decomposes readily at atemperature a little above its melting point and in so doing splits oflammonia, with carbomonophenylimide ((LH N (or its equivalentphenyl-cyanamide or cyanilide), as the main decomposition product, ofvery low melting point and readily polymerizable to a much highermelting point. Its tri-molecular polymerization product being a.melamine with three phenyl substitutions.

Tri-phenyl guanidine, while it does not decompose at as low atemperature as the monophenyl guanidine, nevertheless decomposes readilyat vulcanizing temperatures and splits ofi' aniline, with its maindecomposition product as carbodiphenylimide (C H N (or its equivalentdiphenylcyanamide), also of very low melting point and readilypolymerizable to a much higher melting point. Its tri-molecularpolymerization product being a melamine with six phenyl and either willcombine with more than one phenylguanidine. 1.

Both carbomonophenylimide and carbodiphenylimide form polymerizationproducts which also are more or less reactive with the same bodies astheir lower polymers.

The aniline and ammonia released with these two carbophenylimides isalso reactive with morethan one of the phenylguanidines. In the reactionof mono-phenyl guanidine under vulcanization and with a metallic OX- idepresent, the result appears to be:

Decomposition of the mono-phenyl guanidine, first intocarbomonophenylimide and ammonia, then a dissipation of the ammonia, andthen a gradual combination or polymerization of the carbomonophenylimideinto a phenyl substituted melamine possessing a melting point far abovethat of the product started with, and of considerable stability.

In vulcanizationthen this would indicate an early activity of themono-phenyl guani- (line while the ammonia was being split ofi, then astage where molecules of the carbomonophenylimide were polymerizingtogether, and then an ultimate stage where the progressivepolymerization has resulted in an accumulation of the higher meltingbody as a tri-molecular polymerization product, or melamine of thecarbomonophenylimide, and therefore would be tri-phenyl melamine, andwhich because of its high melting point tends to inhibit furthervulcanization in the cold, and so the resultant rubber compound standsaging better according as this melamine displacesthe other intermediateproducts resulting from the decomposed accelerator.

An illustration of the formation of a phenyl substitutedmelamine isacombining or polymerizing together of three molecules of a phenylsubstituted carbodiimide, and the resultant phenyl substituted melaminewill then contain as many phenyl groups as the three molecules of thephenyl substituted carbodiimide contained.

Carbomonophenylimide is found to be quite active, as more than onemolecule of it will combine together, and it will also combine withcarbodiphenylimide, either as a single molecule of each to producetriphenyl dicarbodiimide melting at to 7 1 C. ((L I I N, Ber. 1887, 20,1065), or as two molecules of the former with one of the latter toproduce tetra-phenyl melamine (C I-I N melting at 217 C. (Ann. 1850,Yet, 6; Ber. 187 1, 7, 1736; Ber. 1875, 8, 912; Monatsh. 1877, 403; Ber.1887, 20,1, 1065).

Carbomonophenylimide will ulso readily combine with aniline to di-phenylguanidine (C I-I N and then in turn can also combine with the di-phenylguanidine to tri-phenyl biguanide (C I-I N Ber. 1890, 28, 1668), meltingat 137 C.

The presence of metallic oxides in a vulca-nization causes thedecomposition or breaking up of these accelerators at temperatures muchlower than would cause the same reactions normally.

In the event that the presence of moisture in these decompositionreactions of the accelerator should cause a molecule of water to unitewith the phenyl substituted carbodiimide, then corresponding phenylureas would form instead, but with sufficient of the amine present, thewater will duly split off again and the product then follow its normalpath of decomposition. Y 1

Many of these reactions are reversible and the temperatures that causethe combination also cause in turn again their disassociation.

Should mono-phenyl guanidine or its disassociation products duringvulcanization form combinations with sulphur or with any of the otherusual compounding constituents, such compounds would appear to belargely catalytic, and rejuvenation of any of them, or of theirdecomposition products later, would permit the normal reactions anddisasso-ciation to continue.

That such reactions do continue has authoritative support, as well asbeing observable in general practice (Ostromuislensky, Jour. Russ. Phys.Chem. Soc. 17, 1892, 8, 1915).

The foregoing relates to mono-phenyl guanidine, to its components, andto its de composition or V disassociation products. However, much thesame series of reactions seem to also take place with the tolyl, xylil,or other substituted guanidines respectively, that are homologo omono-phenyl guanidine, and that limits its members to that serieswhere-in the aryl radicals differ only, in the number of CHsubstitutions in the benzene ring.

While aniline enters into the production of mono-phenyl guanidine, 111 alike manner the homologues of aniline, such as toluidine and Xylidine,bear a similar relation in the production of the corresponding tolyl andXylil substituted guanidines respectively. Mono-substituted guanidineshaving such homologous radicals are then quite suitable for usetogether.

Such a mixture might be desirable, as an accelerator, and if it was inthe form of a solid solution it would permit both guanidines to fimctionat their best under a common melting point.

In my investigation of that series of compounds of which monophenylguanidine, or its equivalent components or disassociation products is anexample, I have found that they prove of unusual value in theacceleration of rubber vulcanization.

Mono-phenyl guanidine is readily made by desulphurizingmono-phenylthiourea in the presence of ammonia (Ber. 1879,12, 1602). Themono-phenylthiourea resulting from a union of phenyl mustard oil andammonia.

Mono-phenyl guanidine is' also made by combining carbomonophenylimideand ammonia (Beilstein, 1883, II, 920). 1

Another way of producing it is from cyanamide ('carbodiimide), andaniline hydrochloride (Am. Chem. Jnl. 1901, 26, 221; Ber. 1904, 37,1681; Richter, 1922, II, 104:). The acid salt of course beingneutralized. V

Mono-phenyl guanidine is also a decomposition product of phenylbiguanide(Monatsh. 1891, 12, 17).

A desulphurization of mono-phenyl thiourea also gives the same phenylsubstituted carbodiimide as does the decomposition of the correspondingmono-phenyl guanidine.

In using mono-phenyl guanidine with the carbomonophenylimide componentor disassociation product, such combination can be a mere mixture, or inthe form of a solid solution, or each may be added separately to therubber mix, and either or both may be used in the rubber mix inconjunction with ammonia;

Any of these means, or any other means for effecting an accelerationactivity of monophenyl guanidine in conjunction withcarbomonophenylimide, or the introduction into a vulcanization of anypolymeric form; of carbomonophenylimide (as easy to obtain or to make asthe guanidine), with ammonia, or

in the presence of any product that will supply ammonia in a manner toeffect a similar reaction activity is intended to be covered by thisspecification.

The mono-substituted guanidines homologous to mono-phenyl guanidine showmuch the samereaction behavior under vulcanizing conditions, because theguanidine nucleus is the same in each and any variation in them is dueto the variation in the aryl amine that supplies the homologous radical.

My invention then consists in making use of these mono-substitutedguanidines and their substituted carbodiimide components anddisassociation products in the vulcanization of rubber, wherein I findthat the result ant vulcanized products are thereby greatly improved.

The quantity of these accelerators to be used in the rubber mix is fromto 1% on the rubber content, and the compounding formula may be any ofthe usual types.

10 to 30% of substituted carbodiimide may be used with the substitutedguanidine, and much larger percents if an aryl amine, or an ammoniagenerating body is also present.

It is to be understood that I do not limit myself to the ingredients,components and proportions given in this specification, or merely tosuch examples as have been cited by me, it being readily understood bythose well versed in the art, that said ingredients, components andproportions may be varied within comparatively wide limits withoutdeparting from the principles and purposes of my invention as herein setforth.

Having now described my invention and having shown in what manner thesame may be utilized, what I claim as new, and desire to secure byLetters Patent is:

1. A process of vulcanizing rubber which consists in, incoporating intocompounded rubber an accelerator, comprising a monophenyl substitutedguanidine combined with a mono-phenyl substituted carbodiimide, thenheating the resultant rubber mixture with a vulcanizing agent to efiectvulcani zation.

2. A process of vulcanizing rubber which consists in incorporating intocompounded rubber an accelerator comprising a monosubstituted guanidinecombined with a monosubstituted carbodiimide that are respectivelyhomologous to mono-phenyl substituted guanidine and mono-phenylsubstituted carbodiimide, then heating the resultant rubber mixture witha vulcanizing agent to effect vulcanization.

3. A vulcanized compound derived from compounded rubber or similarmaterial combined with .a vulcanizing agent and an acceleratorcomprising a mono-phenyl substituted guanidine and a mono-phenylsubstituted carbodiimide.

4. A vulcanized compound derived from compounded rubber or similarmaterial combined with a vulcanizing agent and an accelerator comprisinga mono-substituted guanidine and a mono-substituted carbodiimide thatare respectively homologous to monophenyl substituted guanidine andmonophenyl substituted carbodiimide.

GEORGE H. STEVENS.

